Concurrent transmission of traffic from multiple communication interfaces

ABSTRACT

Line termination units having dual ports for accepting communication traffic of two different types facilitate the concurrent transmission of voice traffic, serial data traffic and packetized data traffic across a telecommunication transport system, such as a DSL (digital subscriber line) system. The bandwidth of the telecommunication transport system is allocated between the differing traffic types to permit the full utilization of the available bandwidth.

RELATED APPLICATIONS

The present invention is a continuation of U.S. application Ser. No.10/008,658 filed on Nov. 9, 2001 now U.S. Pat. No. 7,088,742, which isincorporated herein it its entirety by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to telecommunications, and inparticular to apparatus and methods to facilitate concurrenttransmission of multiple communication protocols across a singlelong-distance communication carrier.

BACKGROUND OF THE INVENTION

A number of communication transport protocols have been defined to carryvoice and/or data traffic across large spans. Two examples of protocolsfor carrying both traditional Pulse Code Modulated (PCM) voice trafficas well as packetized data traffic include the time division multiplexed(TDM) protocols commonly referred to as T1 (United States) and E1(Europe). These two protocols have many similarities, but differsignificantly regarding their respective payload rates. T1 traffic has abit rate of 1544 Kbps divided into 24 timeslots, or channels, of 64 Kbpseach while E1 traffic has a bit rate of 2048 Kbps divided into 32timeslots of 64 Kbps each. An emerging standard for voice and datatraffic is the G.shdsl (ITU G.991.2) standard for SHDSL (single-pairhigh bit-rate digital subscriber line) datalinks, or spans, capable ofbit rates as high as 2304 Kbps, or 36 timeslots of 64 Kbps each.

As telecommunication technology advances, faster transmission rates arefacilitated. However, the latest technology will generally not beimplemented across the board. As such, communication from a sending nodeto a receiving node in a telecommunication transport system may havespans of differing technologies. The interface between various protocolscan result in wasted bandwidth. For example, a SHDSL span would belimited to 1544 Kbps or 2048 Kbps if interposed between two T1 spans ortwo E1 spans, respectively, resulting in a loss of potential bandwidth.

For the reasons stated above, and for other reasons stated below thatwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foralternative apparatus and methods for increasing bandwidth utilizationof telecommunication spans.

SUMMARY

Line termination units are described herein having dual ports foraccepting communication traffic of two different types. The variousembodiments facilitate the concurrent transmission of voice traffic,serial data traffic and packetized data traffic across atelecommunication transport system, such as a DSL (digital subscriberline) system. The bandwidth of the telecommunication transport system isallocated between the differing traffic types to permit the fullutilization of the available bandwidth.

For one embodiment, the invention provides a termination unit for use ina digital subscriber line system. The termination unit includes a firstcommunication interface adapted for receiving first traffic having abandwidth and a second communication interface adapted for receivingsecond traffic different from the first traffic. The termination unitfurther includes a third communication interface for coupling to adigital subscriber line. The termination unit is adapted to combine thefirst traffic received at the first communication interface with thesecond traffic received at the second communication interface, therebygenerating a combined traffic, and to provide the combined traffic tothe third communication interface. The combined traffic has a bandwidthgreater than or equal to the bandwidth of the first traffic.

For another embodiment, the invention provides a termination unit foruse in a digital subscriber line system. The termination unit includes afirst communication interface adapted for receiving first traffic havinga first number of timeslots, each timeslot corresponding to anincremental bit rate, wherein a number (N₁) of timeslots used forpayload is less than or equal to the first number of timeslots. Thetermination unit further includes a second communication interfaceadapted for receiving second traffic, wherein the second traffic has abit rate equal to some multiple (N₂) of the incremental bit rate. Thetermination unit further includes a third communication interface forcoupling to a digital subscriber line and for providing a combinedtraffic having a second number of timeslots, each timeslot correspondingto the incremental bit rate, wherein the second number of timeslots isgreater than or equal to N₁+N₂. The termination unit is adapted to mapthe timeslots of the first traffic to a first portion of the timeslotsof the combined traffic. The termination unit is further adapted to mapthe second traffic to a second portion of the timeslots of the combinedtraffic.

For yet another embodiment, the invention provides a method ofcommunicating across a digital subscriber line system. The methodincludes receiving a first traffic having a bandwidth and receiving asecond traffic different from, and concurrently with, the first traffic.The method further includes combining data of the first traffic with thedata of the second traffic to generate a combined traffic, and providingthe combined traffic to a digital subscriber line of the digitalsubscriber line system.

For still another embodiment, the invention provides a method ofcommunicating across a digital subscriber line system. The methodincludes receiving first traffic having a first number of timeslots,each timeslot corresponding to an incremental bit rate, wherein a number(N₁) of timeslots used for payload is less than or equal to the firstnumber of timeslots. The method further includes receiving secondtraffic, wherein the second traffic has a bit rate equal to somemultiple (N₂) of the incremental bit rate, and combining the firsttraffic and the second traffic to generate a combined traffic having asecond number of timeslots. Each timeslot of the combined trafficcorresponds to the incremental bit rate and the second number oftimeslots is greater than or equal to N₁+N₂. The method still furtherincludes mapping the timeslots of the first traffic to a first portionof the timeslots of the combined traffic and mapping the second trafficto a second portion of the timeslots of the combined traffic.

Further embodiments of the invention include apparatus and methods ofvarying scope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic of a telecommunication transport system inaccordance with an embodiment of the invention.

FIG. 2 is a block schematic of a line termination unit in accordancewith an embodiment of the invention.

FIG. 3 is a block schematic of a synchronizer in accordance with anembodiment of the invention.

FIGS. 4A-4F are depictions of example timeslot assignments in accordancewith embodiments of the invention.

DETAILED DESCRIPTION

In the following detailed description of the present embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process, electrical or mechanical changes may be madewithout departing from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims and equivalents thereof.

The various embodiments facilitate the concurrent transmission of voicetraffic, serial data traffic and packetized data traffic across atelecommunication transport system, such as a DSL (digital subscriberline) system. The bandwidth of the telecommunication transport system isallocated between differing traffic types to permit the full utilizationof the available bandwidth.

FIG. 1 is a schematic of a telecommunication transport system 100 inaccordance with an embodiment of the invention. The system 100 includesa first node 110 and a second node 120 coupled by a span 130. The span130 is a digital subscriber line (DSL) span. For a further embodiment,the DSL span is a single-pair high bit-rate digital subscriber line(SHDSL) span. Such spans typically contain one pair or two pairs oftwisted copper. The first node 110 may be a line termination unit (LTU)located at a central office (CO) of a telecommunication provider whilethe second node 120 may be a network termination unit (NTU) located at acustomer site for interfacing to customer premise equipment (CPE). TheLTU is generally a master device, controlling and monitoring otherunits, such as the NTU.

Although both nodes 110 and 120 are generally adapted for bi-directionalcommunication, FIG. 1 will be discussed with the first node 110 actingas a sending device and the second node 120 acting as a receivingdevice, noting that the roles can be reversed and that thebi-directional communication can occur concurrently.

The first node 110 transmits information to the second node 120 acrossthe span 130 using an appropriate communication protocol. For oneembodiment, the span 130 is a SHDSL span using the G.shdsl standard.Traffic on the span 130 has a bandwidth, or available bit rate, asdefined by its communication protocol. Continuing the G.shdsl example,the maximum bandwidth would be 2304 Kbps as currently defined. As notedearlier, this traffic is divided into 36 timeslots of 64 Kbps each. Theactual bandwidth of the span 130 is determined by the number oftimeslots utilized times the incremental bit rate for each timeslot, inthis case 64 Kbps.

The first node 110 receives the transmission information from multiplecommunication interfaces. A first communication interface 112 is coupledto receive communication traffic of a first type, such as pulse codemodulated (PCM) voice traffic and/or packetized data traffic. This firsttraffic has a bandwidth of less than the maximum bandwidth of the span130. For example, the first communication interface 112 may be aG.703/704 interface coupled to receive E1 traffic having a maximumbandwidth of 2048 Kbps as currently defined. Such E1 traffic is dividedinto 32 timeslots of the incremental bit rate of 64 Kbps each.

Some number (N₁) of the timeslots of the first traffic may be used forapplication data, or payload. The number of timeslots used for payloadmay range from zero (an unused interface) to the total number oftimeslots of the available bandwidth and is user definable. Using E1traffic as an example, between 0 and 32 timeslots may be used forpayload. As currently defined, the first timeslot (timeslot 0) of E1traffic is reserved for framing information unless N₁ is 32, i.e., whereeach timeslot is used for payload. In addition, the seventeenth timeslot(timeslot 16) of E1 traffic is reserved for signaling information unlessN₁ is greater than or equal to 31. The timeslots utilized for payloadmay be contiguous, but there is no requirement to do so. For example,for E1 traffic utilizing 11 timeslots for payload, the payload mayreside in timeslots 1-11. Alternatively, the payload timeslots may benon-contiguous, such as timeslots 4-8, 13-15 and 17-19.

A second communication interface 114 is coupled to receive communicationtraffic of a second type different from the first type. For oneembodiment, the second communication interface 114 is a serial dataportcoupled to receive serial data. For a further embodiment, the secondcommunication interface 114 is an N×64 Kbps interface coupled to receiveserial data having a bandwidth that is some multiple (N₂) of anincremental bit rate, in this case 64 Kbps.

The following discussion will relate to an embodiment of a line atermination unit 200 having an E1 interface as the first communicationinterface 212 and a serial dataport interface as the secondcommunication interface 214 as depicted in FIG. 2. The termination unit200 is adapted for coupling to a DSL. For one embodiment, thetermination unit 200 is adapted for coupling to a SHDSL through anSHSDSL interface as the third communication interface 216.

The E1 interface 212 provides a 2048 Kbps bi-directional digitalinterface for user application data as a PCM data stream. For oneembodiment, it includes an E1 Framer and Line Interface Unit (LIU) 218as well as protection and isolation circuits 220. The E1 interface 212may provide the following controls:

-   -   1) Line coding and decoding according to HDB3.    -   2) Receive frame synchronization: unframed, G.704 (FAS), CRC-4,        CAS Multiframe.    -   3) Timeslot 0 (FAS) regeneration or transparent transmission.    -   4) Optional regeneration of CRC-4 data and framing at the output        data.    -   5) Monitoring of incoming CRC4 errors, Bipolar violations, and        E-bits.    -   6) LOS, LFA, RAI, AIS alarm indication    -   7) Generation of A-bits, E-bits in response to alarms, CRC4        errors    -   8) Transmission of unframed all ones (AIS).    -   9) Diagnostic loopbacks towards and away from the interface    -   10) Programmable Channel blanking and Idle code pattern on        output.

In the receive path, incoming data at the E1 interface 212 may beunframed (i.e. full 2048 Kbps) or framed according to G.704 with 32distinct 64 Kbps channels (8-bit timeslots), and an alternating framealignment (FAS), non-frame alignment word (NFAS) in timeslot 0. Timeslot16 is reserved for network common channel (CCS) or channel associatedsignaling (CAS), and should always be transparently mapped in structuredapplication modes, unless the user selects 31 timeslots assigned to theE1 port.

The serial dataport interface 214 provides a V.35, V.36 (withX.21option), RS-530 or other similar standard N×64 Kbps bi-directionalinterface providing a bandwidth that is some multiple (N₂) of theincremental bit rate of 64 Kbps, such that N₂ ranges from 0 to 36. Thefirmware may monitor and assert the control signals associated with thisinterface and engage loopbacks.

The termination unit 200 further includes a synchronizer 222. Thissynchronizer 222 synchronizes the E1 and serial data flow, presentingthem towards the SHDSL interface 216. The synchronizer 222 may beimplemented as a field-programmable gate array (FPGA),application-specific integrated circuit (ASIC) chip or other controllogic block.

The termination unit 200 further includes a SHDSL chipset 224 formapping the synchronized PCM data stream from the synchronizer 222 intoa SHDSL frame, and for presenting it to the SHDSL interface 216 foroutput over a SHDSL span. In the receive direction, the SHDSL chipset224 presents the data as PCM and narrowband datastreams towards thesynchronizer 222. The synchronizer 222 and SHDSL chipset 224 may beseparate elements as shown in FIG. 2, or their function may be combinedin a single processor block.

For one embodiment, the SHDSL chipset 224 is the CX28975 SHDSL chipsetavailable from Mindspeed Technologies, Newport Beach, Calif., USA. Thischipset has two ports. The first port is referred to as a PCM port. Thesecond port is referred to as a narrowband port. The two ports may becaused to operate simultaneously if a synchronization pulse (sync pulseor framing pulse) on the narrowband port is synchronized with the PCMport. For the Mindspeed chipset, the period of the sync pulse to the PCMport is a multiple of 125 microseconds, typically 2 ms or 6 ms, whilethe period of the sync pulse to the narrowband port is 6 ms. For closesynchronization, e.g., within 100 microseconds, the sync pulseassociated with the narrowband port is generated from the sync pulse forthe PCM port. This process is described in U.S. patent application Ser.No., entitled “Multiple Dataport Clock Synchronization,” which iscommonly assigned and incorporated herein by reference. The sync pulseassociated with the narrowband port is further widened or shortened tobe one narrowband port clock period wide.

The synchronizer 222 and SHDSL chipset 224 may provide the followingfunctionality:

-   -   1) Programming transmit map, route table, receive map and        combine tables including FIFO waterlevels according to desired        application mode.    -   2) Control frame or multiframe synchronization.    -   3) Set SHDSL line rate and frame length    -   4) SHDSL link acquisition and maintenance    -   5) Send and receive EOC messages.    -   6) Monitor SHDSL status: signal-to noise ratio, loop        attenuation, CRC6 errors, far-end-block-errors (FEBE) and remote        alarms.

Data from the E1 interface 212 passes through the synchronizer 222 andis presented to the SHDSL chipset 224 at a first input, or PCM input(not shown in FIG. 2) at a sustained 2048 Kbps bit rate. Serial dataportdata (which may a fractional N×64 k rate) is passed through thesynchronizer 222 and is presented to the SHDSL chipset 224 at a secondinput, or narrowband input (not shown in FIG. 2). The SHDSL chipset 224buffers the PCM and narrowband data and then combines the data into asingle serial data stream for transport across the SHDSL span. It ispreferred that all timeslots of the E1 traffic be mapped contiguouslyonto the single SHDSL span up to the available number of SHDSL payloadtimeslots.

FIG. 3 is a block schematic of a synchronizer 222 in accordance with anembodiment of the invention. Only that portion of the synchronizer 222relating to the interface with the SHDSL chipset 224 will be described.

An interface 330 to the E1 framer and LIU 218 passes through to the PCMport 335 of the SHDSL chipset 224, with the exception of the clocksignal DSL_TPCLK, or master clock, which is provided by a master timingselect circuit.

An interface 340 to the serial dataport interface 214 is passed to thenarrowband port 345 of the SHDSL chipset 224 through a clock and datapolarity control block 350. For one embodiment, the clocking of thenarrowband port 345, via the TNBCLK signal, is generated in N×64Kincrements that is phase locked to the DSL_TPCLK signal. The TNBCLKsignal is also passed through the clock and data polarity control block350 and used to drive the sent timing (DP_ST) signal of the serial dataport. The SHDSL narrowband receive clock (RNBCLK) and data (RNBDAT) arepassed through the clock and data polarity control block 350 to theReceive clock (RT) and data (RD) of the serial dataport. The narrowbandtransmit data (TNBDAT) is driven from the sent data (DP_SD) of theserial dataport.

The serial dataport is capable of accepting data at a N×64K rate. Thisis to say that any multiple of 64 KHz, up to 2304 KHz can be used as theinput clock rate. The Dataport input clock must be locked to theDSL_TPCLK signal to ensure the input/output FIFOs are not over/under runduring a steady state operation or vice-versa. When the N×64 KHzDataport transmit timing clock (DP_TT) is selected as the timingreference for the system, a clock synthesizer circuit is used to createa fixed 2048 KHz reference to output as the DSL_TPCLK. When a sourceother than the DP_TT clock is selected for the system timing reference,the clock synthesizer circuit is used to create a N×64 KHz DP_ST clocksource the serial dataport must use for its timing reference.

For one embodiment, the sync pulse TNBSYNC for the narrowband port 345is derived from the receive multiframe sync pulse E1_RMSYNC from the E1interface 330. The E1_RMSYNC sync pulse is a 2 ms pulse having aduration of approximately 500 nanoseconds. In order to create a 6 mssync pulse, which is required for the narrow band port of the Mindspeedchipset, the E1_RMSYNC sync pulse is first divided down using the fixeddivider 360 to create a 6 ms sync pulse. The resulting intermediate 6 mssync pulse will still have the same duration as the E1_RMSYNC pulse atthis point. This intermediate sync pulse with a 6 ms duration mayoptionally be output to the DSL_TPMSYNC signal (not shown). Theintermediate sync pulse is then widened or shortened using aprogrammable divider 370 to produce the sync pulse TNBSYNC having a 6 msinterval and a duration substantially equal to one clock interval of theclock signal TNBCLK. The narrow band sync pulse TNBSYNC should be phasealigned with the E1_RMSYNC sync pulse output by the E1 framer 218. Thenarrow band sync pulse TNBSYNC should occur within 0-100 microsecondsafter the E1_RMSYNC sync pulse. As the frequency of the narrow bandclock TNBCLK may vary, the value loaded into the divider circuit of theprogrammable divider 370 must also vary. A down counter is used tocreate the programmable divider 370. The equation to calculate thecounter re-load value is: Reload Value=convert to hex(6ms*TNBCLK(freq)−2).

The following tables provide examples of mapping of the combined trafficand accompany FIGS. 4A-4F. In these examples E is for E1 data from thefirst communication interface, D is for dataport data from the secondcommunication interface, F is for framing information (timeslot 0), S isfor signaling information (timeslot 16, if applicable), and X is forunused. Unused timeslots are generally filled with user-defined idlecode. In FIGS. 4A-4F, the top line of each figure corresponds to the DSLmapping of an LTU as a first node while the bottom line of each figurecorresponds to the DSL mapping of an NTU as a second node.

Table 1 is an example of the DSL mapping between two E1 dataports, withFIG. 4A showing example timeslot assignments.

TABLE 1 Side LTU NTU E1 Rate 10 7 E1 Start 1 1 Dataport Rate 0 0Dataport Start 0 0 DSL Rate 12 12

Table 2 is an example of the DSL mapping between two serial dataports,with FIG. 4B showing example timeslot assignments.

TABLE 2 Side LTU NTU E1 Rate 0 0 E1 Start 0 0 Dataport Rate 10 7Dataport Start 0 0 DSL Rate 10 10

Table 3 is an example of the DSL mapping between a serial dataport onone side (the LTU side) and an E1 dataport on the other side (the NTUside), with FIG. 4C showing example timeslot assignments.

TABLE 3 Side LTU NTU E1 Rate 0 7 E1 Start 0 1 Dataport Rate 10 0Dataport Start 0 0 DSL Rate 10 10

Table 4 is an example of the DSL mapping between an E1 dataport on oneside (the LTU side) and a dual port on the other side (the NTU side),with FIG. 4D showing example timeslot assignments.

TABLE 4 Side LTU NTU E1 Rate 17 5 E1 Start 1 1 Dataport Rate 0 10Dataport Start 0 6 DSL Rate 19 19

Table 5 is an example of the DSL mapping between a serial dataport onone side (the LTU side) and a dual port on the other side (the NTUside), with FIG. 4E showing example timeslot assignments.

TABLE 5 Side LTU NTU E1 Rate 0 12 E1 Start 0 1 Dataport Rate 20 8Dataport Start 0 13 DSL Rate 20 20

Table 6 is an example of the DSL mapping between two dual ports, withFIG. 4F showing example timeslot assignments.

TABLE 6 Side LTU NTU E1 Rate 17 13 E1 Start 1 1 Dataport Rate 10 10Dataport Start 19 14 DSL Rate 29 29

CONCLUSION

Line termination units have been described herein having dual ports foraccepting communication traffic of two different types. The variousembodiments facilitate the concurrent transmission of voice traffic,serial data traffic and packetized data traffic across atelecommunication transport system, such as a DSL (digital subscriberline) system. The bandwidth of the telecommunication transport system isallocated between the differing traffic types to permit the fullutilization of the available bandwidth.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any such adaptationsor variations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

1. A termination unit for use in a digital subscriber line system,comprising: a first communication interface receiving first traffichaving a bandwidth; a second communication interface receiving secondtraffic different from the first traffic; and a third communicationinterface for coupling to a digital subscriber line; wherein thetermination unit combines the first traffic received at the firstcommunication interface with the second traffic received at the secondcommunication interface, thereby generating a combined traffic, and toprovide the combined traffic to the third communication interface; andwherein the combined traffic has a bandwidth greater than or equal tothe bandwidth of the first traffic; wherein the second traffic isunframed; wherein the first traffic is frame; wherein the combinedtraffic is framed when the first traffic has a non-zero bandwidth and isunframed when the first traffic has a zero bandwidth.
 2. The terminationunit of claim 1, wherein the first communication interface is aG.703/704 interface.
 3. The termination unit of claim 1, wherein thesecond communication interface is an N×64 Kbps serial dataportinterface.
 4. The termination unit of claim 1, wherein the thirdcommunication interface is a G.shdsl interface.
 5. A termination unitfor use in a digital subscriber line system, comprising: a firstcommunication interface receiving first traffic having a first number oftimeslots, each timeslot corresponding to an incremental bit rate,wherein a number (N₁) of timeslots used for payload is less than orequal to the first number of timeslots; a second communication interfacereceiving second traffic, wherein the second traffic has a bit rateequal to some multiple (N₂) of the incremental bit rate; and a thirdcommunication interface for coupling to a digital subscriber line andfor providing a combined traffic having a second number of timeslots,each timeslot corresponding to the incremental bit rate, wherein thesecond number of timeslots is greater than or equal to N₁+N₂; whereinthe termination unit maps the times lots of the first traffic to a firstportion of the timeslots of the combined traffic; wherein thetermination unit maps the second traffic to a second portion of thetimeslots of the combined traffic; wherein the first portion oftimeslots has a number of timeslots less than or equal to the firstnumber of timeslots and greater than or equal to N₁.
 6. A method ofcommunicating across a digital subscriber line system, comprising:receiving a first traffic having a bandwidth; receiving a second trafficdifferent from the first traffic and concurrently with the firsttraffic; combining data of the first traffic with the data of the secondtraffic, thereby generating a combined traffic; and providing thecombined traffic to a digital subscriber line of the digital subscriberline system; wherein the second traffic is unframed; wherein the firsttraffic is framed; wherein the combined traffic is framed when the firsttraffic has a non-zero bandwidth and is unframed when the first traffichas a zero bandwidth.
 7. The method of claim 6, wherein the firsttraffic is E1 traffic.
 8. The method of claim 6, wherein the secondtraffic is serial data.
 9. The method of claim 6, wherein the digitalsubscriber line is a single-pair high bit-rate digital subscriber line.10. A method of communicating across a digital subscriber line system,comprising: receiving first traffic having a first number of timeslots,each timeslot corresponding to an incremental bit rate, wherein a number(N₁) of timeslots used for payload is less than or equal to the firstnumber of timeslots; receiving second traffic, wherein the secondtraffic has a bit rate equal to some multiple (N₂) of the incrementalbit rate; combining the first traffic and the second traffic to generatea combined traffic having a second number of timeslots, each timeslotcorresponding to the incremental bit rate, wherein the second number oftimeslots is greater than or equal to N₁+N₂; mapping the timeslots ofthe first traffic to a first portion of the timeslots of the combinedtraffic; and mapping the second traffic to a second portion of thetimeslots of the combined traffic; wherein the first portion oftimeslots has a number of timeslots less than or equal to the firstnumber of timeslots and greater than or equal to N₁.